This invention relates to an electronic fuel injection control system for use with an internal combustion engine, and more particularly to an electronic fuel injection control system which is adapted to control the quantity of fuel being injected into an internal combustion engine in dependence upon parameters representing the operating condition of the engine such as intake pressure, throttle valve opening and engine rotational speed.
Conventional electronic fuel injection control systems include a type which is adapted to determine the value of a basic fuel injection quantity on the basis of engine rotational speed, engine intake pressure and/or throttle valve opening, which are parameters representative of the volume of engine intake air.
The systems of this type include a hybrid type which is adapted to determine the value of a basic fuel injection quantity by the use of a matrix memory storing a map which is formed of parameters of engine rpm (hereinafter called "Ne") and intake pressure (hereinafter called "P.sub.B ") in a lower engine load region, while determining the basic fuel injection quantity value by the use of a matrix memory storing a map which is formed of parameters of Ne and throttle valve opening (hereinafter called ".theta.th") in a higher engine load region.
As well known, an internal combustion engine can often suffer poor startability since the engine temperature (hereinafter called "Tw") is low at the start of the engine. To improve the startability, conventional fuel injection control systems employ fuel quantity correction or increase during warming-up of the engine, which comprises correcting the basic injection quantity value which has been determined in the aforementioned manner, in dependence upon the engine temperature from the start of the engine to the completion of the engine warming-up.
In a supercharged engine, the fuel injection quantity is further corrected in dependence upon the mass of intake air. That is, detection is made of the pressure P1 and temperature T1 of intake air, i.e., atmospheric air at the inlet of a compressor located upstream of a throttle valve in the intake pipe of the engine, as well as pressure P2 at a zone between the outlet of the compressor and the throttle valve. Further, the temperature of intake air at the outlet of the compressor is arithmetically determined on the basis of the detected values of the above parameters P1, T1 and P2. Correction of the injection quantity is thus carried out on the basis of the mass of the intake air, i.e., the temperature and pressure of the same thus obtained.
In a non-supercharged engine, similar intake air massbased correction of the injection quantity is employed, using the pressure P1 and temperature T1 of the ambient atmospheric air.
In the above-mentioned conventional electronic fuel injection control systems, control of the fuel injection quantity cannot be properly performed in the event of trouble (breakage, disconnection, shorting, etc.) in the sensors for detecting the various engine operating condition parameters (P.sub.B, .theta.th, Ne, Tw, P1, T1, P2) or in the wires related to the sensors.
For instance, trouble in the engine temperature sensor for detecting the engine temperature (e.g., the temperature of engine cooling water or lubricant oil) and/or its related wiring prevents proper achievement of the aforementioned warming-up fuel quantity increase. More specifically, for instance, if the engine temperature sensor gets broken after completion of the warming-up of the engine so that its output falls in its output range which is usually assumed during warming-up operation, an excessive increase occurs in the quantity of fuel supplied to the engine, resulting in an excessively rich mixture being supplied to the engine. Further, in electronic fuel injection control systems employing the aforementioned hybrid method, the fuel injection control is not properly performed in a lower engine load region in the event of trouble in the P.sub.B sensor or its related wiring, and in a higher engine load region in the event of trouble in the .theta.th sensor or its related wiring, respectively, which can lead to a drop in engine performance. Instead of the hybrid method, a method may be applied to such injection control systems, which comprises determining the value of basic fuel injection quantity throughout the entire engine load regions, by the use of a single matrix memory storing a map formed of parameters of P.sub.B and Ne or a map formed of parameters of .theta.th and Ne. Even in this case, the fuel injection control systems cannot be free of the above-mentioned disadvantage in the event of trouble in the sensors for detecting these parameters or their related wiring. Further, if trouble occurs in the intake air sensor means such as the T1 sensor, the P1 sensor and the P2 sensor or their related wiring, the aforementioned intake air massbased correction cannot be properly performed or is impossible to carry out.